<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>元素居中和外距</title>
    <style>
      article {
        border: solid 3px #ddd;
        width: 800px;
      }
      div {
        border: solid 3px red;
        width: 400px;
         /* 左上 右下 margin: 30px 60px */
        /* 左 上 右 下 margin: 30px 40px 60px 100px; */
       /*  padding: 20px;
        margin-left: 11px;
        margin-top: 12px;
        margin-right: 13px;
        margin-bottom: 14px;*/
        margin: 0 auto;
        /* margin-left: auto;
        margin-right: auto; */

      }
    </style>
  </head>
  <body>
    <article>
      <div>houdunren.com</div>
    </article>
  </body>
</html>
